Extraction Engine: Generate function/property accessor with expression body (whenever applicable)

#KT-6405 Fixed

idea/testData/refactoring/extractFunction/initializers/classes/classInitializer.kt.after

@@ -5,7 +5,5 @@ class A(val a: Int, b: Int) {
         println(i(b) - 1)
     }
 
-    private fun i(b: Int): Int {
-        return a + b
-    }
+    private fun i(b: Int) = a + b
 }

idea/testData/refactoring/extractFunction/initializers/classes/classInitializerWithLambda.kt.after

@@ -5,7 +5,5 @@ class A(val a: Int, b: Int) {
         println({ i(b) - 1 }.invoke())
     }
 
-    private fun i(b: Int): Int {
-        return a + b
-    }
+    private fun i(b: Int) = a + b
 }

idea/testData/refactoring/extractFunction/initializers/classes/classParameters.kt.after

@@ -3,6 +3,4 @@
 val n = 1
 class A(val a: Int, val b: Int = i(a))
 
-private fun i(a: Int): Int {
-    return a + n
-}
+private fun i(a: Int) = a + n

idea/testData/refactoring/extractFunction/initializers/classes/classParametersWithLambda.kt.after

@@ -3,6 +3,4 @@
 val n = 1
 class A(val a: Int, val b: Int = { i(a) }.invoke())
 
-private fun i(a: Int): Int {
-    return a + n
-}
+private fun i(a: Int) = a + n